Many structures, particularly aircraft, require insulation that is both strong and light, and exhibits excellent thermal and acoustic insulative properties. In particular, it is known that a particular type of insulation had excellent characteristics and performance, other than for high heat resistance, for aircraft applications. Such insulation is a rotary fiberized glass insulation, the nature and manufacture of being fully described in U.S. Patent Publication 20070014995, which is fully incorporated herein as if fully rewritten.
In summary, this product and process includes the step of fiberizing molten glass, spraying binder onto the fibers, forming a single component fibrous glass insulation pack on a moving conveyor, and curing the binder on the fibrous glass insulation pack to form an insulation blanket.
More specifically, the glass is first melted in a tank and then supplied to a fiber forming device such as a fiberizing spinner. The spinner is rotated at a high speed so that centrifugal force causes the molten glass to pass through holes in the sidewalls of the spinner to form glass fibers. Single component glass fibers of random lengths may be attenuated from the fiberizing spinner and blown generally downwardly, that is, generally perpendicular to the plane of the spinner by blowers positioned within a forming chamber.
The blowers turn the fibers down to form a veil or curtain. The glass fibers may have a fiber diameter of from about 2 to about 9 microns and a length of from about ¼ inch to about 4 inches. The small diameter of the glass fibers of the insulation as described below helps give the final insulation element a soft feel.
The glass fibers, while still hot from the drawing operation, are sprayed with an aqueous binder composition incorporating an appropriate conventional binder as described above. The glass fibers, with the uncured resinous binder adhered thereto, are then gathered and formed into an uncured insulation pack on an endless forming conveyor within the forming chamber with the aid of a vacuum drawn through the insulation pack from below the forming conveyor. The residual heat from the glass fibers and the flow of air through the insulation pack during the forming operation are generally sufficient to volatilize the majority of the water from the binder before the glass fibers exit the forming chamber, thereby leaving the remaining components of the binder on the fibers as a viscous or semi-viscous high-solids liquid.
The coated insulation pack, which is in a compressed state due to the flow of air through the pack, is then transferred from the forming chamber under exit rollers to a transfer zone where the insulation pack vertically expands due to resiliency of the glass fibers. The expanded insulation pack is the heated, such as by conveying the pack though a curing oven where heated air is blown through the insulation pack to evaporate any remaining water in the binder, cure the binder and residually bond the fibers together.
The cured binder imparts strength and resiliency to the insulation blanket. It is anticipated that the drying and curing of the binder may be carried out in either one or two different steps. If desired, the insulation pack may be compressed by upper and lower oven conveyors in the curing oven in order to form a fibrous insulation blanket of desired thickness. The curing oven may be operated at temperatures from, for example, about 200 to about 325 degrees Celsius. The insulation pack remains within the oven for a period of time sufficient to cross link the binder and form the insulation blanket. Typical residence times in the oven are in the range of about 30 seconds to about 3 minutes. After cooling, the insulation blanket may be rolled by a roll-up device for shipping or for storage for use at a later time. Alternately, the insulation element may be cut to size from the blanket.
If desired, the insulation blanket may be subsequently subjected to an optional needling process in which barbed needles are pushed in a downward and upward motion through the fibers of the insulation blanket to entangle or intertwine the fibers and impart increased mechanical strength and integrity. Needling the insulation blanket also increases the density and reduces the overall thickness of the blanket. The needling process or needle piercing may take place with or without a precursor step of lubricating.
In an alternative approach, glass fibers are processed without adding any aqueous binder composition. In this instance, the glass fibers are bound together using mechanical means including but not limited to needling, stitching and hydroentangling. Further, facings of, for example, glass mat and/or metal foils may be used on one or both sides to secure the fibers for encapsulation.
However, it is well-known in the art that fiberglass products are susceptible to melting and burn-through at high temperatures. Fire is among the deadliest of all possible aircraft tragedies. It is not uncommon for passengers on airplanes to survive an airplane accident, such as crashes, only to perish in the fire that often follows. Such fires may be fueled by spilled jet fuel from ruptured tanks and fuel lines, and is known to burn at temperatures exceeding about 1900 degrees Fahrenheit. Under such heat, the solid aluminum skin of an aircraft may melt in less than about 45 seconds, leaving any survivors directly exposed to such obviously fatal heat.
In an attempt to provide protection, airplanes are typically insulated with composite insulating structures. These structures are placed in assemblies between the structural struts of the aircraft, between the outer airplane skin and the inner passenger surface. Such assemblies typically comprise one more layers of insulating materials, typically with a heat resistive layer at, or near, the aircraft skin. To prevent moisture from entering the insulating material, and to decrease mechanical damage to the insulating material, the assemblies are typically enclosed in a polymer bag.
The FAA has mandated standards for aircraft fire resistance. The FAA test requirements are defined in the Federal Register/Volume 68, No. 147 dated Jul. 31, 2003; 14 C.F.R. Parts 25, 91, 121, 125, and 135; “Improved Flammability Standards for Thermal/Acoustic Insulation Materials Used in Transport Category Airplanes.” In summary; the FAA is adopting upgraded flammability standards for thermal and acoustic insulation materials used in transport category airplanes. These standards include new flammability tests and criteria that address flame propagation and entry of an external fire into the airplane. For airplanes with a passenger capacity of 20 or greater, this final rule requires insulation materials installed in the lower half of the airplane to pass a test of resistance to flame penetration. The test involves exposing samples of thermal/acoustic insulation blankets mounted in a test frame to a burner for four minutes. The insulation blankets must prevent flame penetration for at least four minutes and must limit the amount of heat that passes through the blanket during the test. See final part VII of Appendix F to of 14 C.F.R. Part 25 for more details. The temperature of the flame to which the insulation is exposed is 1900° F., and the maximum allowable heat flux measured on the back side of the test sample during the four minute test is 2 Btu/sq ft-sec.
Various prior art methods have been used, generally with limited success, to meet these FAA requirements, as well as to satisfy the additional acoustic demands made on such insulation.
Numerous methods and structures may provide fire resistance at relatively low temperatures. It has proven considerably more difficult to provide fire resistance to the current level of FAA testing. Additionally, it is noteworthy that fire resistance requires performance involving factors other than pure heat resistance. It is well known that many high-temperature materials become extremely brittle when heated, and the turbulence produced in a real-world fire can be sufficient to destroy the structural integrity of those materials. For example, U.S. Pat. No. 5,766,745 ('745) teaches a carbonaceous textile composite material that was tested to a level of 1000 degrees Celsius, but using a non-turbulent radiant heat plate.
A typical attempt to provide the fire resistance needed in this and similar applications has been to combine a ceramic paper layer with a fibrous layer, for example as taught in U.S. Pat. No. 6,670,291 ('291). Such ceramic papers have inherently low flexibility, and must be made relatively thin, such as the 200 to 450 micron thickness taught as ideal in the '291 patent, and must be kept thin in order to provide acceptable bending parameters. An even thinner fire-resistant aramid-ceramic layer, only 3 to 5 mils thick, is disclosed in U.S. Publ. No. 2006/0046598. These inherently delicate ceramic papers must generally be reinforced with a separate scrim layer to increase the durability of the resultant product.
Another attempt to create an acceptable product in the prior art may be seen in U.S. Pat. No. 6,565,040 ('040). The '040 device uses a multi-layer composite structure where the high temperature resistance is providing by coating or interleaf barrier layer or layers including a reflective plate-like mineral, such as but not limited to vermiculite, applied in a coating to or incorporated into one or both major surfaces of a sheet, such as a paper sheet, an organic fiber mat, a glass fiber mat, or a fabric sheet. Such reflective plate-like minerals again bring with them the inherent disadvantage of weight and brittleness.
Contemplation of the demands of such fire-resistant applications led to the following conclusions: a successful product must display suitable thermal and acoustic insulative properties; must be of high durability; should be of light weight; and should ideally be both dimensionally stable and suitable for mass-production methods, such as die-cutting of component parts. Additionally, all of these requirements must be accomplished at commercially reasonable cost. The instant invention solves these, and many other concerns and problems reflected in the prior art, in a unique and innovative manner.